It is conventional to provide the cleaner head of a vacuum cleaner with an agitator, such as a rotating brush bar, for agitating or “beating” a floor surface—particularly carpet—to improve pick-up performance.
Although the main vac-motor on the cleaner can be used to drive this agitator, it is more common to use a separate, dedicated motor to drive the agitator. This separate motor can then be positioned close to the agitator—usually somewhere on the cleaner head itself—to simplify the transmission arrangement.
In a particularly compact sort of arrangement, the motor is actually housed inside the agitator, which usually takes the form of a hollow cylindrical brush bar. This sort of layout is described in U.S. Pat. No. 6,323,570.
Housing the motor—or part of the motor—within the restricted space inside the agitator makes the motor prone to overheating. Typically therefore, these “motor-in-brushbar” arrangements will incorporate some sort of air-cooling scheme for drawing clean—not dirty—air through the inside of the brush bar to cool the motor.
In the schemes described in U.S. Pat. No. 6,323,570, the cooling air is pulled through the hollow brush bar, which effectively acts as a rotating clean-air duct inside the cleaner head. This arrangement requires an effective dynamic seal to be provided around the brush bar, in order to prevent the dirty air from the main suction chamber being sucked into the motor, through the brush bar.